Luhn check for jQuery-Validation-Engine

validateCreditCard.js

var validateCreditCard = function(field, rules, i, options) {
  var valid = false,
  cardNumber = field.val().replace(/ +/g, "").replace(/-+/g, "");

  var numDigits = cardNumber.length;
  if (numDigits >= 14 && numDigits <= 16 && parseInt(cardNumber) > 0) {
    var pos = 1;
    var luhn = "";
    for (var i = numDigits - 1; i >= 0; i--) {
      var digit = parseInt(cardNumber.charAt(i));
      luhn += (pos++ % 2 == 0) ? digit * 2: digit;
    }
    var sum = 0;
    for (var i = 0; i < luhn.length; i++) {
      sum += parseInt(luhn.charAt(i));
    }
    valid = sum % 10 == 0;
  }
  
  if (!valid) {
    return options.allrules.creditCard.alertText;
  }
}